Workability of Fresh Concrete by Slump Test

WORKABILITY
Slump test is used to determine the workability of fresh concrete. Slump test as per IS: 1199 – 1959 is followed.The apparatus used for doing slump test are Slump cone and Tamping rod.

Procedure to determine workability of fresh concrete by slump test.
i) The internal surface of the mould is thoroughly cleaned and applied with a light coat of oil.
ii) The mould is placed on a smooth, horizontal, rigid and nonabsorbent surface.
iii) The mould is then filled in four layers with freshly mixed concrete, each approximately to one-fourth of the height of the mould.
iv) Each layer is tamped 25 times by the rounded end of the tamping rod (strokes are distributed evenly over the cross section).
v) After the top layer is rodded, the concrete is struck off the level with a trowel.
vi) The mould is removed from the concrete immediately by raising it slowly in the vertical direction.
vii) The difference in level between the height of the mould and that of the highest point of the subsided concrete is measured.
viii) This difference in height in mm is the slump of the concrete.

Reporting of Results
The slump measured should be recorded in mm of subsidence of the specimen during the test. Any slump specimen, which collapses or shears off laterally gives incorrect result and if this occurs, the test should be repeated with another sample. If, in the repeat test also, the specimen shears, the slump should be measured and the fact that the specimen sheared, should be recorded.

Typical Questions Ques 1. What is the ideal value of slump?
Answer 1 In case of a dry sample, slump will be in the range of 25-50 mm that is 1-2 inches. But in case of a wet concrete, the slump may vary from 150-175 mm or say 6-7 inches. So the value of slump is specifically mentioned along the mix design and thus it should be checked as per your location.

Slump depends on many factors like properties of concrete ingredients – aggregates etc. Also temperature has its effect on slump value. So all these parameters should be kept in mind when deciding the ideal slump

Ques 2. How does a superplasticizer effect the slump of concrete?
Answer 2 Value of Slump can be increased by the addition of chemical admixtures like mid-range or high-range water reducing agents (super-plasticizers) without changing the water/cement ratio.

Ques 3. How much time one should take to raise the cone? Answer 3 Once the cone is filled and topped off [ excessive concrete from top is cleared ] raise the cone within 5-10 seconds.

Ques 4. What are the dimensions of the cone used in Slump Test?
Answer 3 The dimensions are
Top Diameter – 10cm
Bottom Diameter – 20cm
Height – 30cm

In general,at what slump value should the concrete cubes be casted at the site if it is coming from a RMC manufacturer. Any specific standards mentioned for the same. If not, if the cubes are casted at a higher slump say 150mm&above or at a relatively lower slump say 100mm&below what effectit will have on the 3,7,&28 days compressive strength of concrete of any grade.

slump is an imp factor in testing of cubes..and slum for residential buildings nearly 80..n slump shall not be less than 60 in any case..and also slum ‘ll be nearly 180 at the time of piling work is done..because for piling more water is requred..

The concrete slump test is, in essence, a method of Becoz,quality control. For a particular mix, the slump should be consistent. A change in slump height would demonstrate an undesired change in the ratio of the concrete ingredients; the proportions of the ingredients are then adjusted to keep a concrete batch consistent. This homogeneity improves the quality and structural integrity of the cured concrete.

Explain why the slump test is the most commonly used consistence.
A concrete mix is found to segregate easily.Describe the steps that can be taken to improve cohesiveness.
Explain what caused the cracking and what could have been done to prevent it.
what is the compaction factor of concrete that is completely self compacting

The slump test is commonly used to assess the workability of the mixture. It is the fastest (and cheapest) way to gauge the consistency of the concrete batches used for placement in structural works. It is NOT a test to gauge the strength of concrete (The typical 3, 7 or 28-day compressive test does that).

A concrete mix found to segregate easily is likely to be too “wet”. Possible solutions are: (1) reduce the water-cement ratio; and (2) if admixtures (superplasticizers) are used, reduce the amount.